Main-chain Liquid Crystalline Polyester Research Articles

Photocatalytic dicarboxylation of strained C[sbnd]C bonds with CO2via consecutive visible-light-induced electron transfer

Dicarboxylic acids have a wide range of applications in the polymer industry to construct valuable materials. Photocatalysis has recently emerged as an efficient and sustainable strategy to generate dicarboxylic acids. However, photocatalytic dicarboxylation with CO2 is mainly limited to unsaturated bonds, and the dicarboxylation of CC single bonds still remains a challenge. Herein, we report a photocatalytic dicarboxylation of CC single bonds in strained rings with CO2 units via consecutive photo-induced electron transfer (ConPET). It is also the first photocatalytic reductive ring-opening reaction of cyclobutanes. Notably, this transition-metal-free protocol exhibits good functional group tolerance, broad substrate scope, facile scalability, and easy product derivatizations. Moreover, diacids can easily be derivatized to main-chain liquid crystalline polyesters.

Molecular-weight dependence of phase structure and viscosity in a liquid crystalline polyester with strong π–π interaction

ABSTRACTIn this article, the molecular-weight dependence of the phase structure, rheological behaviour and thermal stability of a main-chain liquid crystalline polyester (PBDPS) with strong π–π interaction was investigated in details by differential scanning calorimetry, polarising optical microscopy, wide-angle X-ray diffraction, dynamic oscillatory rheological measurements and thermogravimetric analysis. While the molecular weight of PBDPS is 5.2k, it shows smectic B and smectic A phases prior to isotropic phase. With increasing molecular weight, smectic B phase of PBDPS gradually disappeared. Moreover, the smecitc B to smectic A (Tlc) and smectic A to isotropic (Ti) phase transition temperatures decreased as increased molecular weight. The rheology results suggested that fluid type of PBDPSs changed from Newtonian fluid to pseudo-plastic fluid as the molecular weight of PBDPS increased. In addition, the zero-shear viscosity (η0) of PBDPS showed a power law relationship () with molecular weight of PBDPS. All the PBDPSs showed good thermal stability with an initial decomposition temperature higher than 360°C.

Molecular-Weight Dependence of Nucleation Effect of a Liquid Crystalline Polyester β-Nucleating Agent for Isotactic Polypropylene

Unlike low-molecular-weight inorganic or organic nucleating agents (NAs), the physical properties, including phase transition and rheological behaviors, of polymeric NAs are greatly influenced by molecular weight. In this paper, the molecular-weight dependence of the β-nucleation behaviors of a polymeric NA (a main-chain liquid crystalline (LC) polyester, PBDPS) was studied in detail. The nucleation effect of PBDPS on isotactic polypropylene (iPP) shows a strong molecular-weight dependence. Low-molecular-weight PBDPS tended to induce the formation of α-iPP, whereas high-molecular-weight PBDPS tended to induce β-iPP. Moreover, the relative content of β-iPP crystals (kβ) first increased and then decreased as the molecular weight of PBDPS increased, with the maximum value (86.1%) obtained when 2 wt % PBDPS21.2k was incorporated. Furthermore, the stiffness, toughness, and heat distortion temperature (HDT) of iPP were simultaneously improved by incorporating PBDPS.

Nonisothermal Crystallization, Melting Behaviors, and Mechanical Properties of Isotactic Polypropylene Nucleated with a Liquid Crystalline Polymer

The nonisothermal crystallization and melting behaviors of isotactic polypropylene (iPP) nucleated by a main-chain liquid crystalline polyester (poly(4,4′-bis(6-hydroxyhexyloxy)biphenyl phenylsuccinate), PBDPS) as a β-nucleating agent have been investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarizing optical microscopy (POM). The effect of PBDPS on the mechanical properties of iPP was also studied. The results showed that nonisothermal crystallization kinetics of pure iPP and iPP/PBDPS blends can be described by the Jeziorny and Mo methods. PBDPS can induce both α and β crystals for iPP, with β-nucleation playing the more prominent role. The relative content of the β-crystal (kβ) increased as the PBDPS content increased and the cooling rate decreased. The kβ value reached 75%, even with a fast cooling rate of 40 °C/min. The elongation at break, flexural modulus, impact strength, and heat deformation temperature (HDT) are improved by introducing PBDPS, wh...

Chain Folding in Main-Chain Liquid Crystalline Polyester with Strong π–π Interaction: An Efficient β-Nucleating Agent for Isotactic Polypropylene

The influence of the main-chain liquid crystalline polyester (PBDPS) on the crystallization and melting behaviors of isotactic polypropylene (iPP) has been investigated by differential scanning calorimetry (DSC), X-ray diffraction (WAXD), and polarized optical microscopy (POM). The results suggested that PBDPS is an efficient β-nucleating agent for iPP. The melting crystallization temperature as well as β-crystal of iPP increased with increasing of PBDPS content. The relative content of β-iPP crystals (kβ) can reach 96.6% while adding 4% PBDPS during isothermal crystallization at 135 °C. The increased β-nucleation efficiency was ascribed to the adjacent phenyl rings in side groups of PBDPS stacked well together even when the temperature was higher than its clearing point (Ti). Moreover, the distance between stacked phenyls is 0.32 nm, which is half of the unit cell parameter in the c-direction of β-iPP, indicating a lattice match between β-iPP and PBDPS.

Effect of different dimensional carbon nanoparticles on the shape memory behavior of thermotropic liquid crystalline polymer

Different 0D, 1D and 2D carbon nanoparticles were added into a main chain liquid crystalline polyester (LCP) to investigate the effect of the nanoparticles on the shape memory behavior of LCP. Fullerene (C60), multi-wall carbon nanotube (CNT) and graphene (G) were selected as the fillers in an attempt to form π-π interaction with LCP chains, which acted as a physical crosslinking to obtain the increased shape recovery stress and recovery ratio. The composites were prepared by solution mixing. The formation of π-π interaction was investigated by wide angle X-ray diffraction (WXRD), fluorescence emission spectrometry and Raman laser spectrometry. Shape recovery stress and shape recovery ratio were recorded by dynamic mechanical analysis (DMA). Results indicated that C60 and CNT significantly augmented shape recovery ratio but had little effect on Shape recovery stress, while G diminished shape recovery ratio but improved the shape recovery stress.

Fully Liquid-Crystalline ABA Triblock Copolymer of Fluorinated Side-Chain Liquid-Crystalline A Block and Main-Chain Liquid-Crystalline B Block: Higher Order Structure in Bulk and Thin Film States

Fully liquid-crystalline (LC) ABA-type triblock copolymers were synthesized by atom transfer radical polymerization; the A block was a fluorinated side-chain LC polymer, PFA-C8, and the B block was a main-chain LC polyester, BB-5(3-Me). The volume fraction of the A block (φA) was 0.11–0.70, and the B block had a constant molecular weight. Nanometer-scale segregated structures in the bulk and thin film states were investigated by synchrotron X-ray diffraction (XRD) in transmission and grazing-incidence (GI) geometries to examine the effect of competition between the LC orientation and polymer chain dimensions on the morphology. When φA is 0.11, matching of the mesogen orientation in the A and B blocks dominates the main-chain orientation, whereas when φA exceeds 0.28, matching of the lateral dimensions of the A and B blocks dominates the mesogen orientation, although all the polymers showed lamellar structure before isotropization of BB-5(3-Me). GI-XRD revealed that the lamellar structure in the thin film ...

Large spontaneous deformation of uniaxially oriented main-chain liquid–crystalline elastomers composed of BB-n mesogens

ABSTRACTWe observed the spontaneous shape change of a uniaxially oriented liquid–crystalline elastomer composed of smectic main-chain liquid–crystalline polyesters in a cyclic heating–cooling process. Although the elastomer contracted by about 650% on heating up to the isotropic phase, the sample length recovered by about 450% on cooling to room temperature in the first heating–cooling process. In contrast, the elastomer exhibited completely reversible deformation in the second heating–cooling process. The shape change occurred with almost no change in the orientational order of mesogens in the temperature region of the liquid–crystalline phase. The mechanism of the spontaneous thermotropic shape change is discussed.

Optical Behaviors of Cholesteric Liquid-Crystalline Polyester Composites with Various Chiral Photochromic Dopants.

New developments in the field of chiral nematic liquid crystals, such as color displays, are now being widely proposed. This article describes the tunable incident reflection band based on composite materials of low-molecular-weight chiroptical dopants and polymeric networks. These materials have advantages including easily manageable color according to a change in the helical pitch of the cholesteric liquid crystal upon exposure to light. A series of novel chiral dopants of isosorbide derivatives containing photochromic groups and three new main-chain liquid crystalline polyesters were synthesized and identified using nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and elemental analyses. The phase-transition temperatures and the liquid-crystal phase determination of the synthesized polymers were estimated using DSC, WAXD, and POM analyses. The influence of the dopant concentrations and the solubility in a liquid crystalline polymer blend were also studied. The reflection band of the cholesteric liquid crystalline composites could be adjusted and tuned with a wide range of color variation across the entire visible region. A real image recording of the chiral photochromic liquid crystalline polymer blend was achieved by exposing it to UV light through a mask.

Ionic conductivity probed in main chain liquid crystalline azobenzene polyesters

ABSTRACTThree main chain thermotropic liquid crystalline (LC) azobenzene polymers were synthesized using the azobenzene twin molecule (P4P) having the structure Phenylazobenzene‐tetraethyleneglycol‐Phenylazobenzene as the AA monomer and diols like diethylene glycol, tetraethylene glycol (TEG), and hexaethylene glycol as the BB comonomer. Terminal C(O)OMe units on P4P facilitated transesterification with diols to form polyesters. All polymers exhibited stable smectic mesophases. One of the polymers, Poly(P4PTEG) was chosen to prepare composite polymer electrolytes with LiCF3SO3 and ionic conductivity was measured by ac impedance spectroscopy. The polymer/0.3 Li salt complex exhibited a maximum ionic conductivity in the range of 10−5 S cm−1 at room temperature (25 °C), which increased to 10−4 S cm−1 above 65 °C. The temperature dependence of ionic conductivity was compared with the phase transitions occurring in the sample and it was observed that the glass transition had a higher influence on the ionic conductivity compared to the ordered LC phase. Reversible ionic conductivity switching was observed upon irradiation of the polymer/0.3 Li salt complex with alternate UV and visible irradiation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 629–641

Chain folding in main-chain liquid crystalline polyesters: from π–π stacking toward shape memory

A series of main-chain thermotropic liquid crystalline polyesters were synthesized by polycondensation from mesogenic dial such as 4,4′-bis(6-hydroxyhexyloxy)biphenyl (BHHBP) and various diacids with different substituents such as succinic acid (no side group), 2-methylsuccinic acid (aliphatic side group) and 2-phenylsuccinic acid (aromatic side group), named poly(4,4′-bis(6-hydroxyhexyloxy)biphenyl succinate) (PBDS), poly(4,4′-bis(6-hydroxyhexyloxy)biphenyl methylsuccinate) (PBDMS), and poly(4,4′-bis(6-hydroxyhexyloxy)biphenyl phenylsuccinate) (PBDPS), respectively. Liquid crystalline behaviours were investigated through differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and small angle X-ray scattering (SAXS) and the thermal stability of the polyesters was determined via thermogravimetric analysis (TGA). PBDS, PBDMS and PBDPS showed a SmF, SmB and SmA phase, respectively. On enlarging the side group, the d-spacing of the smectic layer increased, indicating folding packing of the polymer chains. Therefore, the adjacent phenyl rings in side groups stacked well together and formed strong π–π interactions even when the temperature was higher than Ti. The special structure of PBDPS could provide good mechanical properties. Thus, PBDPS exhibited the maximum tensile stress (28.6 MPa) and the highest elongation at break (1060%). Furthermore, the strong π–π interaction can act as netpoints; therefore, PBDPS exhibited excellent shape fixing (>99%) and shape recovery ratio (>99%) with large strain (>220%).

Well-Ordered Lamellar Microphase-Separated Morphology of an ABA Triblock Copolymer Containing a Main-Chain Liquid Crystalline Polyester as the Middle Segment 2: Influence of Amorphous Segment Molecular Weight

A series of an ABA triblock copolymer with amorphous polymethacrylate A blocks and a main-chain liquid-crystal (LC) polyester center block were prepared with the molecular weight of the amorphous blocks (Mn am) ranging from 2300 to 10 000 and that of the LC block kept constant at 10 000. Irrespective of asymmetric compositions, all block copolymers invariably formed lamellar microstructures. The LC segments were more extended perpendicular to the interface to form smectic layers parallel to the lamellae and folded to be accommodated in lamellae, whereas the amorphous segments had dimensions similar to those of segments in amorphous block copolymer microdomains. Increases in Mn,am enlarge the interfacial area between the amorphous and LC segments and increase the number of folds in LC segments. Thus, LC lamellar thickness decreases and counterbalances the increase in amorphous lamellar thickness so as to suppress the lamellar spacing increase. When the LC segment was in the isotropic phase, the lamellae in the copolymers at asymmetric fractions were disordered and developed on cooling simultaneously with LC formation. The lamellar formation is attributed to the smectic layers that prefer a flat microdomain interface from an energetic perspective.

Well-Ordered Lamellar Microphase-Separated Morphology of an ABA Triblock Copolymer Containing a Main-Chain Liquid Crystalline Polyester as the Middle Segment

Well-Ordered Lamellar Microphase-Separated Morphology of an ABA Triblock Copolymer Containing a Main-Chain Liquid Crystalline Polyester as the Middle Segment

Control over Internal Structure of Liquid Crystal Polymer Nanofibers by Electrospinning

Liquid crystal polymer nanofibers with a diameter ranging from 0.13 to 4.71 µm were prepared by electrospinning from a main-chain liquid crystalline polyester, BB-5(3-Me). WAXD measurements showed that the formation and orientation of the ordered structure in the electrospun fibers were controlled by the fiber diameter formed during electrospinning. For BB-5(3-Me), the SmA structure with two layer spacings was formed in the fiber during the electrospinning. Under optimal spinning conditions, the SmA structure is highly oriented in the fiber. In addition, annealing transformed the metastable SmA structure in the BB-5(3-Me) fiber into stable SmCA one.

Helical Crystal Assemblies in Nonracemic Chiral Liquid Crystalline Polymers: Where Chemistry and Physics Meet

Chirality transfer (or amplification) in soft materials is an important topic for understanding how chiral assemblies develop from the atomic level to macroscopic objects. This is an interdisciplinary area which is critically associated with the evolution from asymmetric chemistry to asymmetric physics, and, more specifically, in biomaterials, liquid crystals, and polymers. In this review, we discuss our recent studies on the conditions for chirality transfer across different length scales. We observed that the formation of helical structures in different length scales is a typical process in chirality transfer. This is illustrated by a series of nonracemic chiral main-chain liquid crystalline (LC) polyesters, PETs(R*-n). The polymers contained a different number of methylene units in the chain backbone (from 7 to 11). All of the PETs(R*-n) macroscopically exhibited an LC chiral smectic C (SC*) phase, a chiral smectic A (SA*) phase, and a twist grain boundary smectic A (TGBA*) phase with increasing temperature. The atomic chiral centers caused the helical conformation, and then, helical lamellar crystals were found in these polymers. The crystal structures were determined by X-ray diffraction and electron diffraction techniques. Dark field transmission electron microscopic images revealed that the molecular orientation in these helical crystals is double twisted. Our systematic studies showed that chirality transfer from one length scale to another is neither automatic, nor necessary, and it critically depends upon the packing scheme of the chiral building blocks on each length scale. It was particularly surprising that in this series of polyesters, the odd−even effect exists across many length scales. This includes not only thermodynamic properties such as the SC*, the SA*, and the TGBA* LC phase transition temperatures, but also the helical crystal handedness.

Photoactive liquid crystalline polyesters based on bisbenzylidene and pyridine moieties

Abstract Photoactive main chain liquid crystalline polyesters containing bis(benzylidene)acetone and aromatic heterocyclic pyridine were synthesized by solution polycondensation. Chemical structure of monomers and polymers were confirmed by FT-IR, 1 H and 13 C NMR spectroscopy. Thermal property was investigated by TGA and DSC. Optical property of polyesters was studied in chloroform solution and in thin film under UV irradiation and exhibited cis–trans -photoisomerization. This behavior was witnessed by solubility, carbonyl group absorption band in FT-IR, optical microscopy as well as DSC analysis through existence of liquid crystallinity after irradiation of polymers.

Spontaneous deformation of main-chain liquid-crystalline elastomers composed of smectic polyesters

We observe the spontaneous shape change of a uniaxially deformed liquid-crystalline elastomer composed of smectic main-chain liquid-crystalline polyesters in a cyclic heating–cooling process. Although the elastomer contracts by about 115% on heating up to the isotropic phase, the sample length recovers by 55% on cooling to room temperature in the first heating–cooling process, and the elastomer exhibits an almost complete reversible deformation in the second heating–cooling process. By a comparison of the results of sample observation with those of X-ray analysis, we recognise that the strain λ was linearly coupled with the orientational order parameter S. In addition, the results of the X-ray analysis imply that a cybotactic nematic state, in which smectic clusters lie scattered in a nematic-like matrix, emerges after exposure to the isotropic phase.

Photoreactive main chain liquid crystalline polyesters containing oxadiazole and bis(benzylidene) cycloalkanone units

AbstractPhotoreactive main chain liquid crystalline polyesters containing oxadiazole and bis(benzylidene)cycloalkanone moieties were synthesized and characterized by structural, thermal, mesomorphic, and optical measurements. The bis(benzylidene) cycloalkanone chromophores in the main chain can constitute both as a mesogen and photoreactive center, whereas 1,3,4‐oxadiazole is a well‐known fluorophore. The thermal properties of polymers were found to be inversely proportional not only to the spacer length but also to ring‐size of cycloalkanones. Hot stage polarized optical microscopic investigations displayed enantiotropic nematic liquid crystalline phases and development of grainy to schlieren textures depends on the length of flexible spacer in the polymer backbone which was in accordance with DSC analysis. Both photoisomerization and photodimerization are observed from the absorption spectra and discussed. The fluorescence spectra in solution state at various concentrations showed that the polymers show blue‐emission maxima and the Stokes shifts being 48–49 nm. The energy transfer occurred when increasing the concentration of the solution. The band gap energies calculated from the absorption spectra are in the range of 3.17–3.41 eV. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5760–5775, 2008

The photochemistry of some main chain liquid crystalline 4,4′-stilbene dicarboxylate polyesters

Several aspects of the photochemistry and photophysics of four main chain liquid crystalline polyesters with a rigid trans-stilbene 4,4'-dicarboxylate mesogen as chromophore and flexible spacer groups are reported. The three polymers with the longest 'spacer' groups are liquid crystalline at room temperature, two have smectic phases. Chromophore aggregation has a dramatic effect on the photophysics and photochemistry of these polymers. Each of the polymers in poor solvents or as films has greatly perturbed UV-Vis absorption and fluorescence spectra due to aggregation of the stilbene chromophore. These effects are more pronounced upon annealing above the glass transition temperature, T(g), and in the mesophase. Film fluorescence is excitation wavelength dependent and is suppressed at elevated temperatures. The stilbene 'environment' in both films and solution is clearly heterogeneous and energy transfer processes relatively slow. The dominant photochemical reaction upon direct excitation above 300 nm is 2 + 2 photocycloaddition rendering polymer films insoluble. No significant trans-to-cis photoisomerization can be detected upon initial irradiation of the polymer films. There is evidence for the formation of aldehyde and carboxylate functionality upon irradiation in the presence of air. Loss of the aggregate UV-Vis absorption and fluorescence occurs during irradiation. Difference UV-Vis spectra of irradiated films suggest preferential initial consumption of dimeric aggregates. Loss of stilbene UV-Vis absorption upon irradiation above 300 nm can be partly photoreversed upon subsequent 254 nm irradiation. The rate of stilbene chromophore loss from films increased significantly above Tg and in the smectic phase above room temperature.

Structure of Macroscopic Monodomains and Its Soft Confinements of Chiral Smectic Phases on Crystallization in a Main-Chain Nonracemic Liquid Crystalline Polyester

A main-chain nonracemic chiral liquid crystalline (LC) polyester was synthesized using an A−B type condensation reaction of a chiral monomer, R-(−)4‘-{ω-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-heptyloxy}-4-biphenylcarboxylic acid, and was abbreviated as PET(R*-7). Wide-angle X-ray diffraction (WAXD) experiments combined with differential scanning calorimetry measurements revealed multiple phase transitions including a chiral twist grain boundary A (TGBA*) phase, a chiral smectic A (SmA*) phase, a chiral smectic C (SmC*) phase, and a highly ordered monoclinic crystalline (KM) phase with decreasing temperature. Flat-elongated and right-handed double-twisted helical single crystals were grown thermotropically in the smectic LC states. Both crystal types possessed the identical monoclinic unit cell: a = 1.04 nm, b = 0.46 nm, c = 5.59 nm, α = β = 90°, and γ = 84.2° based on the WAXD and selected area electron diffraction results. Uniaxial elongation of centimeter-sized films (along the xz-plane in a th...